Filters are often used in telecommunications and high-frequency technology in contexts where only particular frequency components of a signal are to be processed further. As well as high-pass or low-pass filters, there are also band-pass or band-stop filters. Filters may be implemented digitally and may also be constructed using discrete components. The filters may be constructed on a conductor plate or be formed as coaxial filters in the form of milled or cast cavity structures. Filters of a coaxial construction are mostly produced in a pressure casting method, where fine tuning is possible by means of tuning elements which can additionally be screwed in.
A filter of this type is known for example from DE 10 2004 010 683 B3. However, a filter of this type has the drawback that the construction volume, in particular the height, is large. This leads to problems in some fields of application.
Therefore, the example technology herein provides a coaxial filter having a frame construction in which the ratio of power to construction volume is improved. It should also be possible to construct this filter in as simple and cost-effective a manner as possible.
The coaxial filter has a frame construction comprising at least one filter frame, which consists of an electrically conductive medium and has a receiving space, the receiving space being arranged inside the at least one electrically conductive filter frame. Further, a cover arrangement is provided, which is arranged on two opposing faces of the at least one filter frame, in such a way that the receiving pace is at least predominantly closed on all sides. Exceptions may occur for example in the region of the connection sockets. At least one first resonator internal conductor is arranged in the receiving space. The at least one first resonator internal conductor is galvanically connected to a face of the at least one electrically conductive filter frame, and extends therefrom in the direction of another, in particular opposing face of the electrically conductive filter frame, and ends at a distance from the opposing face of the electrically conductive filter frame and/or is galvanically separated from the opposing face of the electrically conductive filter frame.
It is particularly advantageous that the coaxial filter is constructed in a frame construction, resulting in a very low construction height being achieved. This means that it is possible to see through the high-frequency filter in a plan view thereof when the cover arrangement is removed. The coaxial filter can be produced by casting, in particular by (aluminium or zinc) (pressure) casting. A coaxial filter of this type may be used in particular for powers of 5 to 20 watts. The power may also be lower or higher. The filter frame is preferably formed integrally with the separating web and the resonator internal conductors. A construction in a plurality of parts could also be possible. The resonator internal conductors of the filter frame could also be produced from plastics material, which would thus have to be provided with an electrically conductive layer.
An example coaxial filter comprises at least one electrically conductive separating web, which originates on a first face of the at least one filter frame and is galvanically conductively connected to said frame, and protrudes into the receiving space, and extends in the direction of a second face of the at least one filter frame where it ends so as to form an opening therewith, causing the receiving space to be divided into at least one first and at least one second receiving chamber and the opening connecting the two receiving chambers. The at least one first resonator internal conductor is arranged in the at least one first receiving chamber of the receiving space. The at least one first resonator internal conductor is galvanically connected either to a third face of the at least one electrically conductive filter frame or to a first face of the electrically conductive separating web, and extends therefrom either in the direction of the separating web or in the direction of the filter frame, and ends at a distance from the separating web or filter frame and is galvanically separated therefrom. The same also applies to a second resonator internal conductor, which is arranged in the second receiving chamber of the receiving space.
The coaxial filter comprises in particular a first coupling-in and/or coupling-out device and/or at least a second coupling-in and/or coupling-out device, which, from the outside, preferably via the first face of the at least one filter frame, enters the first or second receiving chamber, where it establishes predominantly capacitive or predominantly inductive coupling to the associated first or second resonator internal conductor. It is also possible for a third coupling-in and/or coupling-out device to be arranged opposing the first or second coupling-in and/or coupling-out device, this preferably being arranged on the second face, which is opposite the first face. This can thus establish predominantly capacitive or predominantly inductive coupling to a first resonator internal conductor and/or a second resonator internal conductor in the first or second receiving chamber, the resonator internal conductor being arranged in the associated receiving chamber closest to the third coupling-in and/or coupling-out device. The third coupling-in and/or coupling-out device preferably passes through the opening. The coupling-in and/or coupling-out devices may also be arranged on the third or fourth face.
One end of the at least one first resonator internal conductor, which end is not galvanically connected to the filter frame or to the at least one separating web, comprises an extension portion in the direction of the first and/or second face of the filter frame, resulting in the at least one first resonator internal conductor being formed L-shaped or T-shaped in a plan view. This extension portion preferably extends exclusively parallel to the third or fourth face of the filter frame or parallel to the separating web. It could also extend at an inclination to the third or fourth face of the filter frame. The same also applies to the at least one second resonator internal conductor. This may also comprise an extension portion of this type. As a result, the electrically effective length of the associated resonator internal conductor is increased. At the same time, the capacitive coupling between the resonator internal conductor may also be extended towards the filter frame or the separating web via the extension portion.
The extension portions of all of the first resonator internal conductors or all of the second resonator internal conductors can thus all point in the same direction. They can also be orientated differently from one another.
So as to increase the inductive coupling between two adjacent resonator internal conductors, the adjacent resonator internal conductors can be galvanically connected via a coupling web. This coupling web may be arranged at a distance both from the filter frame and from the separating web. However, it should be arranged on the end of the resonator internal conductors at which the adjacent resonator internal conductor are galvanically connected to the filter frame and the separating web. The coupling web could also be galvanically connected to the filter frame or the separating web at the face thereof facing the filter frame or the separating web.
At least one capacitive and/or inductive coupling is provided between two resonator internal conductors which are non-adjacent or not consecutive on the signal transmission path.
Coupling of this type is preferably provided in the spacing region between the resonator internal conductors and the cover arrangement. An inductive coupling between the two resonator internal conductors is spaced apart from the other resonator internal conductors (positioned below) and from the cover arrangement. A capacitive coupling is spaced apart from all of the resonator internal conductors and from the cover arrangement. The capacitive coupling preferably has a larger area at the resonator internal conductors which are to be coupled than at the other resonator internal conductors.
The coaxial filter comprises a plurality of filter frames which are arranged above one another. The cover arrangement closes off the outer filter frame from the outside and comprises at least one intermediate cover. In each case, at least one intermediate cover is arranged between every two filter frames and separates them from one another. However, the intermediate cover comprises at least one coupling opening, through which coupling between at least two resonator internal conductors of different filter frames is provided. As a result, cascading can be provided or the individual filter paths can be extended.